The Geometry Editor is used to create and define geometry datasets, which are a crucial component of water quality modeling. Users create a geometry dataset and link it to an ResSim Network (created in the Reservoir Network module as described in the HEC-ResSim User's Manual) and the HEC-RAS Geometry (refer to the HEC-RAS User's Manual). This chapter provides detailed instructions on how to create, define, and modify water quality geometry datasets.